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All of the following are examples of the evidence that supports the endosymbiotic theory EXCEPT A. Mitochondria and chloroplasts divide in a process resembling binary fission. B. Mitochondria and chloroplasts are similar in size to bacteria. C. Mitochondria and chloroplasts have linear chromosomes. D. Mitochondria and chloroplasts have their own genomes.

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Answer:

All of the following are examples of the evidence that supports the endosymbiotic theory EXCEPT for option C. Mitochondria and chloroplasts have linear chromosomes.

Explanation:

The endosymbiotic theory essentially states that some organules of the eukaryotic cells, such as mitochondria and chloroplasts, were once free-living bacteria. Probably, these organisms must have been phagocytosed, but not digested by another cell. On the contrary, these bacteria were able to adapt to their host so that the two cells established a dependent relationship with each other.

Due to its similarities to other free-living bacteria, it is speculated that chloroplasts must derive from cyanobacteria and that mitochondria must derive from rickettsias.

This theory is supported by a few characteristics of the chloroplasts and mitochondria that suggest they were once a free cell. For example,

  • Both organelles present their own genetic material. This DNI is bi-catenary and circular, identical to the bacterial DNA, and very different from the eukaryotic cell´s DNA.
  • These organelles divide by binary fission (not by mitosis) and can synthesize their own ribosomes and organelles.
  • Both organelles present a double membrane, a characteristic that reinforces the idea of being phagocyted. The internal membrane looks identical to the bacterial membrane, while the external membrane looks like the eukaryotic one.
  • The sizes of the organelles are similar to the size of some procaryotes.

 

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